American Concrete Institute (ACI) Practice Exam

How many strokes are required per layer when rodding the sample?

20 15 30 25

Correct Answer:

Explanation:

Consolidating freshly mixed concrete in a mold uses a specific number of strokes per layer to ensure the specimen has uniform density without causing segregation. The standard practice for preparing strength test cylinders is to rod each layer a fixed number of times, and fifteen strokes per layer is the commonly recommended count. Performing 15 strokes per layer properly compacts the concrete, helps eliminate entrapped air, and produces a representative density throughout the mold. If you used more strokes, you risk overworking the mix, pushing mortar and fines, or creating surface voids; fewer strokes can leave voids and inconsistent density. By sticking to fifteen strokes per layer, you achieve reliable, consistent specimens for strength testing.

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